Machines, simple

Photo by: Vladislav Kochelaevs

A simple machine is a device for doing work that has only one part. Simple
machines redirect or change the size of forces, allowing people to do work
with less muscle effort and greater speed, thus making their work easier.
There are six kinds of simple machines: the lever, the pulley, the wheel
and axle, the inclined plane, the wedge, and the screw.

Everyday work

We all do work in our daily lives and we all use simple machines every
day. Work as defined by science is force acting upon an object in order to
move it across a distance. So scientifically, whenever we push, pull, or
cause something to move by using a force, we are performing work. A
machine is basically a tool used to make this work easier, and a simple
machine is among the simplest tools we can use. Therefore, from a
scientific standpoint, we are doing work when we open a can of paint with
a screwdriver, use a spade to pull out weeds, slide boxes down a ramp, or
go up and down on a see-saw. In each of these examples we are using a
simple machine that allows us to achieve our goal with less muscle effort
or in a shorter amount of time.

Earliest simple machines

This idea of doing something in a better or easier way or of using less of
our own muscle power has always been a goal of humans. Probably from the
beginning of human history, anyone who ever had a job to do would
eventually look for a way to do it better, quicker, and easier. Most
people
try to make a physical job easier rather than harder to do. In fact, one
of our human predecessors is called
Homo habilis,
which means "handy man" or "capable man."
This early version of our human ancestors was given that name because,
although not quite fully human, it had a large enough brain to understand
the idea of a tool, as well as hands with fingers and thumbs that were
capable of making and using a tool. Therefore, the first simple machine
was probably a strong stick (the lever) that our ancestor used to move a
heavy object, or perhaps it was a sharp rock (the wedge) used to scrape an
animal skin, or something else equally simple but effective. Other early
examples might be a rolling log, which is a primitive form of the wheel
and axle, and a sloping hill, which is a natural inclined plane. There is
evidence throughout all early civilizations that humans used simple
machines to satisfy their needs and to modify their environment.

Words to Know

Compound machine:
A machine consisting of two or more simple machines.

Effort force:
The force applied to a machine.

Fulcrum:
The point or support on which a lever turns.

Resistance force:
The force exerted by a machine.

Work:
Transfer of energy by a force acting to move matter.

The beauty of simple machines is seen in the way they are used as
extensions of our own muscles, as well as in how they can redirect or
magnify the strength and force of an individual. They do this by
increasing the efficiency of our work, as well as by what is called a
mechanical advantage. A mechanical advantage occurs when a simple machine
takes a small "input" force (our own muscle power) and
increases the magnitude of the "output" force. A good
example of this is when a person uses a small input force on a jack handle
and produces an output force large enough to easily lift one end of an
automobile. The efficiency and advantage produced by such a simple device
can be amazing, and it was with such simple machines that the rock statues
of Easter Island, the stone pillars of Stonehenge, and the Great Pyramids
of Egypt were constructed. Some of the known accomplishments of these
early users of simple machines are truly amazing. For example, we have
evidence that the builders
of the pyramids moved limestone blocks weighing between 2 and 70 tons
(1.8 and 63.5 metric tons) hundreds of miles, and that they built ramps
over 1 mile (1.6 kilometers) long.

Trade-offs of simple machines

One of the keys to understanding how a simple machine makes things easier
is to realize that the amount of work a machine can do is equal to the
force used, multiplied by the distance that the machine moves or lifts the
object. In other words, we can multiply the force we are able to exert if
we increase the distance. For example, the longer the inclined
plane—which is basically a ramp—the smaller the force needed
to move an object. Picture having to lift a heavy box straight up off the
ground and place it on a high self. If the box is too heavy for us to pick
up, we can build a ramp (an inclined plane) and push it up. Common sense
tells us that the steeper (or shorter) the ramp, the harder it is to push
the object to the top. Yet the longer (and less steep) it is, the easier
it is to move the box, little by little. Therefore, if we are not in a
hurry (like the pyramid builders), we can take our time and push it slowly
up the long ramp to the top of the shelf.

Understanding this allows us also to understand that simple machines
involve what is called a "trade-off." The trade-off, or the
something that is given up in order to get something else, is the increase
in distance. So although we have to use less force to move a heavy object
up a ramp, we have increased the distance we have to move it (because a
ramp is not the shortest distance between two points). Most primitive
people were happy to make this trade-off since it often meant being able
to move something that they otherwise could not have moved.

Today, most machines are complicated and use several different elements
like ball bearings or gears to do their work. However, when we look at
them closely and understand their parts, we usually see that despite their
complexity they are basically just two or more simple machines working
together. These are called compound machines. Although some people say
that there are less than six simple machines (since a wedge can be
considered an inclined plane that is moving, or a pulley is a lever that
rotates around a fixed point), most authorities agree that there are in
fact six types of simple machines.

Lever

A lever is a stiff bar or rod that rests on a support called a fulcrum
(pronounced FULL-krum) and which lifts or moves something. This may
be one of the earliest simple machines, because any large, strong stick
would have worked as a lever. Pick up a stick, wedge it under one edge of
a rock, and push down and you have used a lever. Downward motion on one
end results in upward motion on the other. Anything that pries something
loose is also a lever, such as a crow bar or the claw end of a hammer.
There are three types or classes of levers. A first-class lever has the
fulcrum or pivot point located near the middle of the tool and what it is
moving (called the resistance force). A pair of scissors and a seesaw are
good examples. A second-class lever has the resistance force located
between the fulcrum and the end of the lever where the effort force is
being made. Typical examples of this are a wheelbarrow, nutcracker, and a
bottle opener. A third-class lever has the effort force being applied
between the fulcrum and the resistance force. Tweezers, ice tongs, and
shovels are good examples. When you use a shovel, you hold one end steady
to act as a fulcrum, and you use your other hand to pull up on a load of
dirt. The second hand is the effort force, and the dirt being picked up is

This man is demonstrating the use of a lever (the board) and fulcrum.
(Reproduced by permission of

Photo Researchers, Inc.

)

the resistance force. The effort applied by your second hand lies between
the resistance force (dirt) and the fulcrum (your first hand).

Pulley

A pulley consists of a grooved wheel that turns freely in a frame called a
block through which a rope runs. In some ways, it is a variation of a
wheel and axle, but instead of rotating an axle, the wheel rotates a rope
or cord. In its simplest form, a pulley's grooved wheel is attached
to some immovable object, like a ceiling or a beam. When a person pulls
down on one end of the rope, an object at the opposite end is raised. A
simple pulley gains nothing in force, speed, or distance. Instead, it only
changes the direction of the force, as with a Venetian blind (up or down).
Pulley systems can be movable and very complex, using two or more
connected pulleys. This permits a heavy load to be lifted with less force,
although over a longer distance.

Wheel and axle

The wheel and axle is actually a variation of the lever (since the center
of the axle acts as the fulcrum). It may have been used as early as 3000
B.C.
, and like the lever, it is a very important simple machine. However,
unlike the lever that can be rotated to pry an object loose or push a load
along, a wheel and axle can move a load much farther. Since it consists of
a large wheel rigidly attached to a small wheel (the axle or the shaft),
when one part turns the other also does. Some examples of the wheel and
axle are a door knob, a water wheel, an egg beater, and the wheels on a
wagon, car, or bicycle. When force is applied to the wheel (thereby
turning the axle), force is increased and distance and speed are
decreased. When it is applied to the axle (turning the wheel), force is
decreased and distance and speed are increased.

Inclined plane

An inclined plane is simply a sloping surface. It is used to make it
easier to move a weight from a lower to a higher spot. It takes much less
effort to push a wheel barrow load slowly up a gently sloping ramp than it
does to pick it up and lift it to a higher spot. The trade-off is that the
load must be moved a greater distance. Everyday examples are stairs,
escalators, ladders, and a ship's plank.

Wedge

A wedge is an inclined plane that moves and is used to increase
force—either to separate something or to hold things together. With
a
wedge, the object or material remains in place while the wedge moves. A
wedge can have a single sloping surface (like a door stop that holds a
door tightly in place), or it can have two sloping surfaces or sides (like
the wedge that splits a log in two). An axe or knife blade is a wedge, as
is a chisel, plow, and even a nail.

Screw

A screw can be considered yet another form of an inclined plane, since it
can be thought of as one that is wrapped in a spiral around a cylinder or
post. In everyday life, screws are used to hold things together and to
lift other things. When it is turned, a screw converts rotary (circular)
motion into a forward or backward motion. Every screw has two parts: a
body or post around which the inclined plane is twisted, and the thread
(the spiraled inclined plane itself). Every screw has a thread, and if you
look very closely at it, you will see that the threads form a tiny
"ramp"

The gears that power a film projector.
(Reproduced by permission of

Thomas Video

.)

that runs from the tip to the top. Like nails, screws are used to hold
things together, while a drill bit is used to make holes. Other examples
of screws are airplane and boat propellers.

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